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Discussion Starter · #1 ·
Actually having to work on my own house for a change!! My generac guardian 43902 will run fine for hours then raise voltage up to 180 or so, on each leg to N. It then goes offline (still running, no voltage at transfer switch/panel) after about 30 seconds then comes back on at high voltage, cycles this way until I shut it down. I can hear it load and unload. This is with no load on, all breakers off. Transfer SW isn't trying to change or anything like that. Once I leave it off for a hour, it comes back on at 120/240 or at least in normal range. Then does it all again after a while. It is running smooth, no crazy idle or anything. I don't work on generators usually so I'm trying to save myself some troubleshooting time.
 

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Wellp, for starters its a generac...

I would say voltage regulator, however does the gen display any error codes? Does it produce 180 under load?
 

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I assume this is one of the older rectangular mechanically governed units? The voltage regulators are available. Getting yourself one of the service manuals is helpful too.
 

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Discussion Starter · #4 ·
Yeah, the old school box type. It's not throwing any codes. Just spoke w/ another EC who is a generac guy. He told me to test from 0 to 4 terminals on the voltage reg. if it's less than 22 ohms were are good. Also that the brushes can cause the regulator to go out. Gonna check all that later today. Any other ideas?
 

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Yeah, the old school box type. It's not throwing any codes. Just spoke w/ another EC who is a generac guy. He told me to test from 0 to 4 terminals on the voltage reg. if it's less than 22 ohms were are good. Also that the brushes can cause the regulator to go out. Gonna check all that later today. Any other ideas?
Sounds like you're gas is high octane. Try buying the mid grade about 89!:jester:
 

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It probably doesn't hurt to take a look at the brush holder and make sure its in good shape. I use some of that green scoth brite stuff to clean slip rings. Odd that it works for a while and then it changes.
 

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It probably doesn't hurt to take a look at the brush holder and make sure its in good shape. I use some of that green scoth brite stuff to clean slip rings. Odd that it works for a while and then it changes.
Sounds like something is heating up, an intermittent problem. I would run it under loads then go ahead with measurements after it kicks out.
 

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I was thinking the same thing and its always a question of whether the single component is bad and or something else damaged it. At least if all that's wrong is a bad VR, they are available and easily replaced.
 

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Discussion Starter · #9 ·
I got a set of brushes and a voltage regulator. I just haven't had time to install it. Too busy running around putting meter cans and masts up for folks. My power was restored so it's no rush. Oddly enough it ran fine the last day and a half, so surge, nothing. I think some generator/generac classes are in my future.
 

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The classes are well taught, though they will likely focus on newer units. Pick their brains while you are there. Changing the VR anyway due to age might not be a bad idea anyway. Replaced a Briggs VR yesterday, it was kicking out 300v. 7 years old.
 
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